This invention relates to electromechanical systems and techniques for fabricating microelectromechanical and/or nanoelectromechanical systems; and more particularly, in one aspect, to fabricating or manufacturing microelectromechanical and/or nanoelectromechanical systems having a mechanical structure encapsulated using thin film or wafer bonding encapsulation techniques and electrical charge supplied to, stored on and/or trapped on one or more portions of the structure.
Microelectromechanical systems (“MEMS”), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques.
MEMS often operate through the movement of certain elements or electrodes, relative to fixed or stationary electrodes, of the mechanical structures. This movement tends to result in a change in gap distances between moving electrodes and stationary or fixed electrodes (for example, the gap between opposing electrodes). (See, for example, U.S. Pat. Nos. 6,240,782, 6,450,029, 6,500,348, 6,577,040, 6,624,726, and U.S. Patent Applications 2003/0089394, 2003/0160539, and 2003/0173864). For example, the MEMS may be based on the position of a deflectable or moveable electrode of a mechanical structure relative to a stationary electrode.
The mechanical structures are typically sealed in a chamber. The delicate mechanical structure may be sealed in, for example, a hermetically sealed metal container (for example, a TO-8 “can”, see, for example, U.S. Pat. No. 6,307,815), bonded to a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082), or encapsulated by a thin film using micromachining techniques during, for example, wafer level packaging of the mechanical structures. (See, for example, International Published Patent Applications Nos. WO 01/77008 A1 and WO 01/77009 A1).
In the context of the hermetically sealed metal container, the substrate on, or in which the mechanical structure resides may be disposed in and affixed to the metal container. The hermetically sealed metal container also serves as a primary package as well.
In the context of the semiconductor or glass-like substrate packaging technique, the substrate of the mechanical structure may be bonded to another substrate whereby the bonded substrates form a chamber within which the mechanical structure resides. In this way, the operating environment of the mechanical structure may be controlled and the structure itself protected from, for example, inadvertent contact. The two bonded substrates may or may not be the primary package for the MEMS as well.
Thin film wafer level packaging employs micromachining techniques to encapsulate the mechanical structure in a chamber using, for example, a conventional oxide (SiO.sub.2) deposited or formed using conventional techniques (i.e., oxidation using low temperature techniques (LTO), tetraethoxysilane (TEOS) or the like). (See, for example, WO 01/77008 A1, FIGS. 2-4). When implementing this technique, the mechanical structure is encapsulated prior to packaging and/or integration with integrated circuitry.
MEMS have been proposed for a variety of miniaturized systems. For example, miniaturized systems have been proposed to provide distributed sensing capability. In some such systems, miniaturized sensors monitor conditions and transmit signals back to a host receiver. Such systems may prove useful in many applications including for example, automotive tires, homeland security industrial monitoring and weather prediction. However, such systems require electrical power in order to operate.
Current miniature battery technology provides enough energy to power many of such systems, at least for a period of time. It would be desirable, however, to have the ability to power such systems for a longer period of time without the need to replace the electrical power source.
In that regard, it has been proposed to power such systems utilizing energy from the environment (sometimes referred to as “energy scavenging” or “energy harvesting”). Some of the most common sources of such energy are vibrational energy, stress (pressure) energy and thermal energy. Of these, vibrational energy may be the most readily available.
To that effect, methods have been proposed to use MEMS to convert vibrational energy into electrical energy. One such method proposes to use a MEMS having a variable capacitor formed of movable semiconductor plates. Electrical charge is placed on the plates of the variable capacitor. Thereafter, when vibrational energy causes the plates to move apart, the variable capacitor produces electrical energy. The electrical energy can be stored and/or used to power one or more devices and/or systems.
One roadblock to implementing such a method has been a difficulty encountered in trying to retain the electrical charge on the plates of the capacitor. For example, contaminants within the chamber can result in leakage currents that quickly drain the electrical charge from the plates of the capacitor.
There is a need for, among other things, a MEMS and/or a technique for fabricating a MEMS that overcomes one, some or all of the shortcomings described above. There is a need for, among other things, a MEMS having a mechanical structure that is encapsulated using thin film encapsulation and/or wafer bonding techniques and that possesses an improved ability to store charge. There is a need for, among other things, a MEMS having a mechanical structure that is encapsulated using wafer level thin film and/or wafer bonding encapsulation techniques, and include one or more structures for use in storing charge within such MEMS.